NASA’s Juno Spacecraft Exploring Jupiter’s Inner Moons During Extended Mission

After revealing a trove of details about the Jovian moons Ganymede and Europa, the mission to Jupiter is setting its sights on sister moon Io.

Today (December 15), as part of its continuing exploration of Jupiter’s inner moons, NASA’s Juno mission is scheduled to obtain images of the Jovian moon Io, the most volcanically active world in the Solar System. Now in the second year of the solar-powered spacecraft’s extended mission to investigate the interior of Jupiter, Juno performed a close flyby of Ganymede in 2021 and of Europa earlier this year.

“The team is really excited to have Juno’s extended mission include the study of Jupiter’s moons. With each close flyby, we have been able to obtain a wealth of new information,” said Juno Principal Investigator Scott Bolton of the Southwest Research Institute in San Antonio. “Juno sensors are designed to study Jupiter, but we’ve been thrilled at how well they can perform double duty by observing Jupiter’s moons.”

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This animation illustrates how the magnetic field surrounding Jupiter’s moon Ganymede (represented by the blue lines) interacts with and disrupts the magnetic field surrounding Jupiter (represented by the orange lines). Credit: NASA/JPL-Caltech/SwRI/Duling

Numerous papers based on the June 7, 2021, Ganymede flyby were recently published in the Journal of Geophysical Research: Planets, Journal of Geophysical Research: Space Physics, and Geophysical Research Letters. They include findings on the moon’s interior, surface composition, and ionosphere, along with its interaction with Jupiter’s magnetosphere, from data obtained during the flyby. Preliminary results from Juno’s September 9 flyby of Europa include the first 3D observations of Europa’s ice shell.

Below the Ice

During the flybys, Juno’s Microwave Radiometer (MWR) added a third dimension to the mission’s Jovian moon exploration: It provided a groundbreaking look beneath the water-ice crust of Ganymede and Europa to obtain data on its structure, purity, and temperature down to as deep as about 15 miles (24 kilometers) below the surface.

Visible-light imagery obtained by the spacecraft’s JunoCam, as well as by previous missions to Jupiter, indicates Ganymede’s surface is characterized by a mixture of older dark terrain, younger bright terrain, and bright craters, as well as linear features that are potentially associated with tectonic activity.

This illustration depicts NASA’s Juno spacecraft soaring over Jupiter’s south pole. Credit: NASA/JPL-Caltech

“When we combined the MWR data with the surface images, we found the differences between these various terrain types are not just skin deep,” said Bolton. “Young, bright terrain appears colder than dark terrain, with the coldest region sampled being the city-sized impact crater Tros. Initial analysis by the science team suggests Ganymede’s conductive ice shell may have an average thickness of approximately 30 miles or more, with the possibility that the ice may be significantly thicker in certain regions.”

Magnetospheric Fireworks

During the spacecraft’s June 2021 close approach to Ganymede, Juno’s Magnetic Field (MAG) and Jovian Auroral Distributions Experiment (JADE) instruments recorded data showing evidence of the breaking and reforming of magnetic field connections between Jupiter and Ganymede. Juno’s ultraviolet spectrograph (UVS) has been observing similar events with the moon’s ultraviolet auroral emissions, organized into two ovals that wrap around Ganymede.

JunoCam took this image of Jupiter’s northernmost cyclone (visible to the right along the bottom edge of image) on September 29, 2022. Credit: Image data: NASA/JPL-Caltech/SwRI/MSSSImage processing by Navaneeth Krishnan S CC BY 3.0

“Nothing is easy – or small – when you have the biggest planet in the solar system as your neighbor,” said Thomas Greathouse, a Juno scientist from SwRI. “This was the first measurement of this complicated interaction at Ganymede. This gives us a very early tantalizing taste of the information we expect to learn from the JUICE” – the ESA (European Space Agency) JUpiter ICy moons Explorer – “and NASA’s Europa Clipper missions.”

Volcanic Future

Jupiter’s moon Io, the most volcanic place in the solar system, will remain an object of the Juno team’s attention for the next year and a half. Their Dec. 15 exploration of the moon will be the first of nine flybys – two of them from just 930 miles (1,500 kilometers) away. Juno scientists will use those flybys to perform the first high-resolution monitoring campaign on the magma-encrusted moon, studying Io’s volcanoes and how volcanic eruptions interact with Jupiter’s powerful magnetosphere and aurora.

References:

“Juno’s Close Encounter With Ganymede—An Overview” by C. J. Hansen, S. Bolton, A. H. Sulaiman, S. Duling, F. Bagenal, M. Brennan, J. Connerney, G. Clark, J. Lunine, S. Levin, W. Kurth, A. Mura, C. Paranicas, F. Tosi, P. Withers, 12 December 2022, Geophysical Research Letters.
DOI: 10.1029/2022GL099285

“Global Modeling of Ganymede’s Surface Composition: Near-IR Mapping From VLT/SPHERE” by Oliver King and Leigh N. Fletcher, 12 December 2022, Journal of Geophysical Research: Planets.
DOI: 10.1029/2022JE007323

“Ganymede’s auroral footprint latitude: Comparison with magnetodisc model” by T. Promfu, J. D. Nichols, S. Wannawichian, J. T. Clarke, M. F. Vogt and B. Bonfond, 12 December 2022, Journal of Geophysical Research: Space Physics.
DOI: 10.1029/2022JA030712

“Magnetic Field Conditions Upstream of Ganymede” by Marissa F. Vogt, Fran Bagenal and Scott J. Bolton, 12 December 2022, Journal of Geophysical Research: Space Physics.
DOI: 10.1029/2022JA030497

“Ganymede MHD Model: Magnetospheric Context for Juno’s PJ34 Flyby” by Stefan Duling, Joachim Saur, George Clark, Frederic Allegrini, Thomas Greathouse, Randy Gladstone, William Kurth, John E. P. Connerney, Fran Bagenal, Ali H. Sulaiman, 12 December 2022, Geophysical Research Letters.
DOI: 10.1029/2022GL101688

“In situ ion composition observations of Ganymede’s outflowing ionosphere” by P.W. Valek, J. H. Waite, F. Allegrini, R. W. Ebert, F Bagenal, S. J. Bolton, J. E. P. Connerney, W. S. Kurth, J. R. Szalay and R.J. Wilson, 12 December 2022, Geophysical Research Letters.
DOI: 10.1029/2022GL100281

“UVS Observations of Ganymede’s Aurora During Juno Orbits 34 and 35” by T. K. Greathouse, G. R. Gladstone, P. M. Molyneux, M. H. Versteeg, V. Hue, J. A. Kammer, M. W. Davis, S. J. Bolton, R. S. Giles, J. E. P. Connerney, J.-C. Gerard, D. C. Grodent, B. Bonfond, J. Saur and S. Duling, 12 December 2022, Geophysical Research Letters.
DOI: 10.1029/2022GL099794

“Evidence for Magnetic Reconnection at Ganymede’s Upstream Magnetopause During the PJ34 Juno Flyby” by R. W. Ebert, S. A. Fuselier, F. Allegrini, F. Bagenal, S. J. Bolton, G. Clark, J. E. P. Connerney, G. A. DiBraccio, W. S. Kurth, S. Levin, D. J. McComas, J. Montgomery, N. Romanelli, A. H. Sulaiman, J. R. Szalay, P. Valek and R. J. Wilson, 12 December 2022, Geophysical Research Letters.
DOI: 10.1029/2022GL099775

“Juno Magnetometer Observations at Ganymede: Comparisons With a Global Hybrid Simulation and Indications of Magnetopause Reconnection” by N. Romanelli, G. A. DiBraccio, R. Modolo, J. E. P. Connerney, R. W. Ebert, Y. M. Martos, T. Weber, J. R. Espley, W. S. Kurth, F. Allegrini, P. Valek and S. J. Bolton, 12 December 2022, Geophysical Research Letters.
DOI: 10.1029/2022GL099545

“Ganymede’s UV Reflectance From Juno-UVS Data” by P. M. Molyneux, T. K. Greathouse, G. R. Gladstone, M. H. Versteeg, V. Hue, J. Kammer, M. W. Davis, S. J. Bolton, R. Giles, J. E. P. Connerney, J. C. Gérard and D. C. Grodent, 12 December 2022, Geophysical Research Letters.
DOI: 10.1029/2022GL099532

“Gravity Field of Ganymede After the Juno Extended Mission” by L. Gomez Casajus, A. I. Ermakov, M. Zannoni, J. T. Keane, D. Stevenson, D. R. Buccino, D. Durante, M. Parisi, R. S. Park, P. Tortora and S. J. Bolton, 12 December 2022, Geophysical Research Letters.
DOI: 10.1029/2022GL099475

“Ganymede Observations by JunoCam on Juno Perijove 34” by M. A. Ravine, C. J. Hansen, G. C. Collins, P. M. Schenk, M. A. Caplinger, L. Lipkaman Vittling, D. J. Krysak, R. P. Zimdar, J. B. Garvin and S. J. Bolton, 12 December 2022, Geophysical Research Letters.
DOI: 10.1029/2022GL099211

“Surface Features of Ganymede Revealed in Jupiter-Shine by Juno’s Stellar Reference Unit” by Heidi N. Becker, Meghan M. Florence, Martin J. Brennan, Candice J. Hansen, Paul M. Schenk, Michael A. Ravine, John K. Arballo, Scott J. Bolton, Jonathan I. Lunine, Alexandre Guillaume and James W. Alexander, 12 December 2022, Geophysical Research Letters.
DOI: 10.1029/2022GL099139

“Updated Spherical Harmonic Magnetic Field Moments of Ganymede From the Juno Flyby” by Tristan Weber, Kimberly Moore, John Connerney, Jared Espley, Gina DiBraccio, Norberto Romanelli, 12 December 2022, Geophysical Research Letters.
DOI: 10.1029/2022GL098633

“Alternating North-South Brightness Ratio of Ganymede’s Auroral Ovals: Hubble Space Telescope Observations Around the Juno PJ34 Flyby” by Joachim Saur, Stefan Duling, Alexandre Wennmacher, Clarissa Willmes, Lorenz Roth, Darrell F. Strobel, Frédéric Allegrini, Fran Bagenal, Scott J. Bolton, Bertrand Bonfond, George Clark, Randy Gladstone, Thomas K. Greathouse, Denis C. Grodent, Candice J. Hansen, William S. Kurth, Glenn S. Orton, Kurt D. Retherford, Abigail M. Rymer and Ali H. Sulaiman, 12 December 2022, Geophysical Research Letters.
DOI: 10.1029/2022GL098600

“Energetic Charged Particle Observations During Juno’s Close Flyby of Ganymede” by G. Clark, P. Kollmann, B. H. Mauk, C. Paranicas, D. Haggerty, A. Rymer, H. T. Smith, J. Saur, F. Allegrini, S. Duling, R. W. Ebert, W. S. Kurth, R. Gladstone, T. K. Greathouse, W. Li, F. Bagenal, J. E. P. Connerney, S. Bolton, J. R. Szalay, A. H. Sulaiman, C. J. Hansen and D. L. Turner, 12 December 2022, Geophysical Research Letters.
DOI: 10.1029/2022GL098572

“Ganymede’s Radiation Cavity and Radiation Belts” by P. Kollmann, G. Clark, C. Paranicas, B. Mauk, D. Haggerty, A. Rymer and F. Allegrini, 12 December 2022, Geophysical Research Letters.
DOI: 10.1029/2022GL098474

More About the Mission

NASA’s Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology (Caltech) in Pasadena, California, manages the Juno mission for the principal investigator, Scott J. Bolton, of the Southwest Research Institute in San Antonio. Juno is part of NASA’s New Frontiers Program, which is managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington. Lockheed Martin Space in Denver built and operates the spacecraft.